The growth of high quality oxides of silicon on silicon wafers is a fundamental and critical aspect of semiconductor chip fabrication. Several different methods are currently used to create oxide layers on silicon wafers.
The highest quality oxides are those grown thermally, as opposed to those which are deposited. The growth time of a thick oxide typically follows a square law, where the final thickness of the oxide is a function of the square of the total oxidation time. Thus, the time required to grow a thick oxide layer can rapidly become commercially unrealistic, forcing manufacturers to use deposited oxide layers, which are typically of lower quality.
High temperature oxidation increases the growth rate of the oxide but can cause other problems. Dopant diffusion occurs much more rapidly at elevated temperatures, which can negatively affect the electrical performance of the chips being fabricated at the same time that a thicker oxide layer is being created. As the square law is still in effect, even at elevated temperatures, the thickness of the oxide grown is still a function of the square of the oxidation time.
High pressure oxidation also allows faster growth of the oxide layer. However, this type of processing requires a special furnace, capable of withstanding the high pressures used for the oxide layer growth. As the square law remains in effect, the thickness of the oxide layer is still a function of the square of the oxidation time.
A faster growing but lower quality oxide can be created by depositing low density, amorphous silicon and oxidizing it. However, such layers require special processing machines to deposit the low density silicon. The growth of these oxide layers still obeys the previously mentioned square law and does not result in a layer whose planarity is acceptable without additional processing.
The aforementioned methods to grow or deposit oxide layers create decidedly non-planar oxide layers. These non-planar oxide layers must be further processed to obtain the degree of planarity needed to fabricate working integrated circuits ("IC"s). These additional processing steps are complicated and add to the expense of fabricating the ICs.
A method for producing thermally grown, reasonably planar thick oxide layers economically would be a valuable advance in semiconductor chip fabrication.